Effects of different lipid contents on growth of earthworms and the products during vermicomposting.

In China, the production of kitchen waste was more than 97 million tons per year in 2016. The high lipid content of kitchen waste makes it hard to degrade. Vermicomposting is a kind of low-cost biotechnology through the combination of earthworms and microbes, which could be considered in converting kitchen waste to valuable products. However, the effect of the lipid in kitchen waste on earthworms and composting is not known yet. The objective of this study was to analyze the effects of lipid on vermicomposting and to derive the most suitable lipid content in vermicomposting. In our study, kitchen waste with four different lipid contents was prepared: 0% (A), 5% (B), 10% (C) and 15% (D). The earthworm growth and chemical characters of substrates were measured at the interim (14 days) and the end (28 days) of vermicomposting. Our results showed that the high content of lipid had negative effects on growth of earthworms and products in vermicomposting. The kitchen waste with lower lipid content could be better composted by earthworms. The average body weight of the earthworm increased by 9% in treatment A. Total nitrogen, available phosphorus, available potassium and nitrate nitrogen of treatment A with 0% (measured value: 5%) lipid content were significantly higher than those in other treatments. Meanwhile, treatment A had the lowest carbon/nitrogen ratio which might be due to hindrances in the breathing and activities of earthworms. The high content of lipid makes growth of aerobic bacteria such as nitrifying bacteria difficult.